md.man

   1 MD(4)                                                       MD(4)
   2
   3
   4
   5 N\bNA\bAM\bME\bE
   6        md - Multiple Device driver aka Linux Software Raid
   7
   8 S\bSY\bYN\bNO\bOP\bPS\bSI\bIS\bS
   9        /\b/d\bde\bev\bv/\b/m\bmd\bd_\bn
  10        /\b/d\bde\bev\bv/\b/m\bmd\bd/\b/_\bn
  11
  12 D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
  13        The  m\bmd\bd  driver  provides virtual devices that are created
  14        from one or more  independant  underlying  devices.   This
  15        array  of devices often contains redundancy, and hence the
  16        acronym RAID which stands for a Redundant Array  of  Inde-
  17        pendant Devices.
  18
  19        m\bmd\bd support RAID levels 1 (mirroring) 4 (striped array with
  20        parity device) and 5 (striped array with distributed  par-
  21        ity  information.   If  a  single  underlying device fails
  22        while using one of these level, they array  will  continue
  23        to function.
  24
  25        m\bmd\bd  also  supports a number of pseudo RAID (non-redundant)
  26        configuations  including  RAID0  (striped  array),  LINEAR
  27        (catenated array) and MULTIPATH (a set of different inter-
  28        faces to the same device).
  29
  30
  31    R\bRA\bAI\bID\bD S\bSU\bUP\bPE\bER\bR B\bBL\bLO\bOC\bCK\bK
  32        With the exception of Legacy Arrays described below,  each
  33        device  that is incorportated into an MD array has a _\bs_\bu_\bp_\be_\br
  34        _\bb_\bl_\bo_\bc_\bk  written  towards  the  end  of  the  device.   This
  35        superblock  records  information  about  the structure and
  36        state of the array so that the array an  be  reliably  re-
  37        assembled after a shutdown.
  38
  39        The  superblock  is  4K  long  and  is  written into a 64K
  40        aligned block that start at least 64K and less  than  128K
  41        from the end of the device (i.e. to get the address of the
  42        superblock round the size of the device down to a multiple
  43        of 64K and then subtract 64K).  The available size of each
  44        device is the ammount of space before the super block,  so
  45        between 64K and 128K is lost when a device in incorporated
  46        into an MD array.
  47
  48        The superblock contains, among other things:
  49
  50        LEVEL  The
  51
  52        UUID   a 128 bit Universally Unique Identifier that  iden-
  53               tifies the array that this device is part of.
  54
  55
  56    L\bLI\bIN\bNE\bEA\bAR\bR
  57    R\bRA\bAI\bID\bD0\b0
  58    R\bRA\bAI\bID\bD1\b1
  59    R\bRA\bAI\bID\bD4\b4
  60    R\bRA\bAI\bID\bD5\b5
  61    R\bRE\bEB\bBU\bUI\bIL\bLD\bD/\b/R\bRE\bES\bSY\bYN\bNC\bC
  62 F\bFI\bIL\bLE\bES\bS
  63        /\b/p\bpr\bro\boc\bc/\b/m\bmd\bds\bst\bta\bat\bt
  64               Contains  information about the status of currently
  65               running array.
  66
  67        /\b/p\bpr\bro\boc\bc/\b/s\bsy\bys\bs/\b/d\bde\bev\bv/\b/r\bra\bai\bid\bd/\b/s\bsp\bpe\bee\bed\bd_\b_l\bli\bim\bmi\bit\bt_\b_m\bmi\bin\bn
  68               A readable and writable file that reflects the cur-
  69               rent  goal rebuild speed for times when non-rebuild
  70               activity is current on an array.  The speed  is  in
  71               Kibibytes per second, and is a per-device rate, not
  72               a per-array rate (which means that  an  array  with
  73               more  disc  will  shuffle  more  data  for  a given
  74               speed).   The default is 100.
  75
  76
  77        /\b/p\bpr\bro\boc\bc/\b/s\bsy\bys\bs/\b/d\bde\bev\bv/\b/r\bra\bai\bid\bd/\b/s\bsp\bpe\bee\bed\bd_\b_l\bli\bim\bmi\bit\bt_\b_m\bma\bax\bx
  78               A readable and writable file that reflects the cur-
  79               rent  goal  rebuild  speed  for  times when no non-
  80               rebuild activity  is  current  on  an  array.   The
  81               default is 100,000.
  82
  83
  84 S\bSE\bEE\bE A\bAL\bLS\bSO\bO
  85        m\bmd\bda\bad\bdm\bm(8), m\bmk\bkr\bra\bai\bid\bd(8).
  86
  87
  88
  89                                                             MD(4)